Recently, there has been progressed a development of a curative treatment for breast cancer by radiation of particle beam such as proton beam and heavy particle beam. It is preferable for this radiation therapy with proton beam to keep breasts to be treated away from a chest wall as much as possible to avoid a negative effect to a part other than the breasts due to the radiation with proton beam. To achieve this, it is required for the patient to be secured holding a state of drooping the breasts at an abdominal position. Meanwhile, for radiation with proton beam or heavy particle beam, the patient needs to be at a supine position. Therefore, for the radiation therapy with proton beam or heavy particle beam, an operating table configured to rotate the patient with a head-feet direction as a rotation axis is necessary.
As the operating table configured to secure and hold the patient in the rotated state, as disclosed in Patent Document 1, there has been known the following therapeutic bed. The therapeutic bed is constituted of a base frame and a platform that turns a patient around a rotation axis along a head-feet direction with respect to the base frame.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-516719